1. Field of the Invention
The present invention relates to a core structure of a heat exchanger that includes tubes and corrugated fins arranged alternatively between the seat plates connected by reinforcements.
2. Description of the Related Art
A core structure of a heat exchanger of this kind is disclosed in Japanese patent laying-open publication No. (Hei) 11-14285. This core structure of the heat exchanger is constructed so that tubes and corrugated fins are alternately arranged between seat plates and both edge portions are coupled and reinforced by reinforcements.
Further, another conventional core structure of a heat exchanger is disclosed in Japanese utility model laying-open publication No. (Hei) 02-54076. This core structure of the heat structure is used for hybrid electric vehicles or the like, and has the core structure similar to the above conventional one, while it has two tanks attached to seat plates and two core parts for cooling coolants with different temperature or different kind of coolant.
The above known conventional core structures of the heat exchanger, however, encounter a problem that edge portions, especially contacting portions with the seat plates, of the tubes have a tendency to be cracked due to rapid changes in temperature from low to high of the coolant flowing through the tubes.
Ordinarily, the rapid changes in temperature hardly occurs, while rapid change of coolant flowing an engine into a radiator in temperature from low to high occurs, for example, in a case that when the engine is started in a cold region, coolant of the engine increases gradually in temperature but does not flow into the radiator until it reaches a valve-opening temperature of a thermostat, and then the temperature of the coolant becomes high to cause a valve of the thermostat to open, so that the coolant of high temperature flows into the radiator for the first time, or in a case of hunting phenomena such that the thermostat repeats opening and closing. This results in repeated change of thermal expansion and construction in longitudinal and thickness directions of the tubes. In this case, the tubes arranged at the outermost positions of the seat plates are restricted in their thermal expansions in the thickness direction by the reinforcements, thermal stresses due to the differences between the thermal expansion amounts of the tubes, the reinforcements, and the seat plates concentrate on seat-plate contacting portions of the outermost positioned tubes to cause the contacting portions to crack.
Incidentally, the heat exchanger used in a hybrid electric vehicle or the like has the tubes that are arranged at outermost positions of the two core parts, and especially adjacent tubes of the core parts are applied by strong thermal stress to be cracked because of coolants with different temperatures flowing in the tubes.
In order to avoid the above problem, there is a case that dummy tubes sealed at their end portions are used at the outermost positions of seat plates, which brings the heat changer degradation of heat exchanging performance and enlargement of its dimensions.
It is, therefore, an object of the present invention to provide a core structure of a heat exchanger which overcomes the foregoing drawbacks and can avoid occurrence of a crack in a seat-plate contacting portion of a tube arranged at an outermost position of the seat plate without degradation of heat exchanging performance and enlargement of dimensions of a heat exchanger.